A vehicle door is usually provided with an impact beam to protect occupants from an impact of a side collision. The impact beam extends along the longitudinal direction of a vehicle, and absorbs an impact load applied to a side portion of the vehicle. An example of the vehicle door provided with such an impact beam is described in Japanese Patent Application Publication No. 2003-211961 (JP-A-2003-211961).
The vehicle door is provided with a lateral beam, which extends along the width direction of the vehicle door (i.e. the longitudinal direction of the vehicle), and a branch beam. The lateral beam and the branch beam are fixed to fixing portions that are fixed to the main body of the vehicle door. The lateral beam and the branch beam are disposed at different positions in the height direction of the vehicle door. Therefore, the area in which the beams are present becomes wider in the height direction of the vehicle door. As a result, the protective area in the vehicle door, which is protected by the beams, is widened in the height direction of the vehicle door.
However, the vehicle door described in Japanese Patent Application Publication No. JP-A-2003-211961 requires two beams, that is, the lateral beam and the branch beam. This increases the number of vehicle door components and complexity in the structure of the vehicle door.